1. Field of the Invention
This invention relates to lens mountings, and more particularly to the control of focusing and aperture setting by a common built-in reversible motor.
2. Description of the Prior Art
(1) The use of the conventional electric motor for operating the focusing mechanism with its layout inside the common casing of the lens mounting has been shown in many patents. Most of them and the methods employed in commercially available cameras are directed to provide auto-focus apparatus in which the period of energization of the motor is automatically controlled in accordance with the signal from the in-focus detector, while motion of the motor is transmitted through a gear train and rack-pinion connection or the like by axial movement of the focusing lens holder until the focusing lens reaches to the in-focus position. U.S. Pat. Nos. 4,274,735 and 4,422,740 are prior art documents which belong to the above-described category (1).
(2) A document which is concerned with known motor-built-in lens mounting is the specification of U.S. Pat. No. 4,152,060 (Japanese Patent Publication No. Sho 56-51328). The motorized focusing apparatus of this patent comprises a lens holder having a central axis substantially coincident with an optical axis of a lens contained therein, a stator concentric to the aforesaid optical axis, an epicyclic motor having a cylindrical armature in eccentric relation to the aforesaid optical axis upon actuation to epicyclically rotate, a transmission carrying the aforesaid lens holder rotatably in the interior of the aforesaid cylindrical armature and in concentric relation to the aforesaid optical axis upon rotation to move the aforesaid lens holder axially, and a drive connection between the armature and the transmission. Thus, this U.S. Patent uses a novel motor in which the rotor is provided with a central opening of sufficiently large diameter to admit of the light beam of the focusing lens.
The lens mounting is provided with a motor in which the rotor and stator are formed to the hollow core shape, and the inner diameter of the rotor is sufficient to admit the image bearing beam (electromagnetic drive device). There are known so-called accidental motion compensation type lens mountings, examples of which are shown in U.S. Pat. Nos. 3,311,747 and 3,552,834.
In the present state of the art of camera systems camera bodies and interchangeable lenses, there is a trend of increasing the proportion of electronic parts. In terms of lens mountings, too, the operating systems for focusing, zooming and aperture setting are being changed from requiring the help of the operator's hand to full automation using an electric motor. To impart automatic focusing and automatic diaphragm setting capabilities into the lens mounting in such a trend, if separate motors are employed, a problem arises in the design of lens mounting mechanisms.
That is, when the focusing lens and the diaphragm are driven by respective individual motors, the bulk, size, and weight of the lens mounting unit are objectionably increased, since good portability, minimum size, and light weight are essential to the candid camera.
A first object of the present invention is to provide a mechanical mounting for an objective with only one motor to carry out two different operations (focusing and diaphragm setting), since the direction of rotation of the motor is reversed.
Another object of the present invention is to provide a drive system for the mounting mechanism in which only one motor, upon rotation in one direction, effects automatic focusing and, upon rotation in the reversed direction, effects, automatic setting of the diaphragm aperture.
Still another object of the present invention is to provide the rotor of the aforesaid motor with a central aperture opening of a sufficiently large diameter to admit the image forming light beam from the focusing lens and to provide a mounting mechanism with means for transmitting the rotating torque of the aforesaid rotor to axial movement of the focusing lens and menas, while maintaining the focusing lens in focus, for moving the diaphragm device to the setting by the aforesaid motor, and particularly to obtain a lens mounting unit having no awkward projection due to the incorporated motor protruding from the outer barrel, or having a uniform outer appearance.